1. Field of the invention
The present invention relates to satellite systems, and more particularly, reflectors for satellite systems.
2. Description of the related art
A reflector, commonly called a dish, is generally a parabolic section having a round or elliptical configuration. A reflector functions to gather radio or microwave frequency energy transmitted from the feedhorn or through the ambient environment from an external transmitter. The reflector can thus be used to receive and transmit signals to and from the satellite system. Reflectors are usually located outdoors, where snow and ice may collect on the receiving or concave side, degrading the performance of the reflector.
It is known to heat the front surface of a reflector with an embedded heater wire. The heater wire is held in place by heat staking the polyvinylchloride (PVC) wash coating a fiberglass cloth to an extruded PVC jacket that insulates the heater wire. A problem with this method is that the extruded PVC jacket thermally insulates the heater wire, inhibiting the heat from the wire from reaching the front surface of the reflector and thereby reducing the thermal efficiency of the heater wire. Another problem with embedding a heater wire within a reflector in a conventional manner is that heat is convected through the reflector to the back surface thereof. The heat is then radiated directly to the ambient environment, resulting in a further reduced thermal efficiency of the heater wire.
It is also known to mold heater wire into the back side of the reflector. That is, the heater wire is molded into the reflector closer to the back surface of the reflector than to the front surface. A problem with this method is that much heat is lost through the back surface of the reflector to the ambient environment.
Additionally, it is known to embed heating electrodes within a reflector. Both the reflecting surface and the electrodes are formed from electrically conductive materials, and it is thus necessary to provide a layer of insulating resin material between the reflecting surface and the electrodes. This insulating material actually decreases the thermal efficiency of the electrodes. Moreover, as with other known reflector assemblies employing embedded heaters, no insulation is provided on the back of the reflector to inhibit heat transfer to the ambient environment.
It is further known to provide a reflector assembly with a reflector which is spaced apart from and connected with a back cover. The reflector and back cover define an enclosed air chamber therebetween. A radiant heater is placed within the air chamber adjacent the back cover and radiates heat to the entire back surface of the reflector to melt or inhibit the accumulation of ice and snow on the reflector. Alternatively, forced hot air may be circulated within the air chamber between the reflector and back cover. The inside surface of the back cover may include a layer of fiberglass insulation and/or a reflective surface to radiate heat towards the reflector.
A reflector assembly used in conjunction with a back cover as described above uses convection or radiation to heat the back surface of the reflector. Such a heating technique is effective to heat the entire back surface of the reflector when desirable for certain applications, but is somewhat inefficient since the back surface of the reflector must be heated via convection or radiation and the heat then transferred to the front surface of the reflector via conduction. This means that the back surface of the reflector must actually be heated above a desired operating temperature on the front surface of the reflector due to thermal losses resulting from the conduction heat transfer. Moreover, the back cover is spaced apart from the reflector and increases the effective size of the reflector assembly, requiring additional space for operation and rendering handling more cumbersome.
Further, it is known to energize heater wire for a reflector with power line voltage, with 120 and 240 volts being common in the United States. A problem is that power line voltage varies widely through out the world. A different heater configuration is required to accommodate each different power line voltage.
What is needed in the art is an improved heater assembly which inhibits or melts ice accumulation on the front surface of a reflector using embedded heater wire, reduces the amount of heat lost through the back surface of the reflector, and accommodates a variety of power line voltages.